In recent years, the technology of hot rolling has made remarkable progress. This has given an impetus to the development of certain high-quality hot-rolling rolls, each of which has an outer layer composed according to a high-speed steel composition (those rolls being referred to hereinbelow as high-speed steel rolls), the outer layer being capable of affording abrasion resistance to a markedly improved extent that is derivable from addition of V and W in large amounts and from subsequent crystallization of a hard carbide of V and a hard carbide of W (for instance, Japanese Unexamined Patent Publication No. 1-96355, No. 6-145888, No. 4-80344, No. 5-1350, No. 5-5155, No. 8-35033 and the like). Part of such rolls have now been put to practical use.
However, from the points of view of quality rise and efficient productivity concerning rolled products, those environmental conditions under which hot-rolling rolls are employed have become more and more strict, simultaneously with severe surface qualities required for rolled steel plates. Still further improvements, therefore, need to be made with respect to the abrasion resistance and surface quality of such a hot-rolling roll. Owing to incorporation with a variety of alloy components such as V, W, Mo, Cr and so on, a high-speed steel roll has two or more different carbides crystallized depending upon the amount of each element used (those carbides being MC, M.sub.6 C, M.sub.7 C.sub.3, M.sub.2 C, M.sub.3 C and so on). In addition, the carbides are formed more increasingly with increases of the amounts of the above alloy elements. This is taken to indicate that there is a strong likelihood of abrasion resistance being further improved in an appropriate range of compositions. However, in the case where many different carbides are caused to form in large amounts in a cast roll so as to attain enhanced abrasion resistance of the latter, such carbides become remarkably segregated during solidification because of their varying levels of crystallization timing and also of their varying specific gravities with the consequence that the resultant roll undergoes, on its surface, patterns of segregation in the course of hot rolling. In particular, the roll when applied to one for a subsequent finish mill leaves the problem that a steel plate to be rolled suffers impaired surface quality.
Here, in the production of a high-speed steel roll through a centrifugal casting method of economical advantage in respect of production cost, this method requires applied centrifuge force and involves prolonged solidification, thus tending to cause carbides to be more frequently segregated than other methods. On the other hand, when a high-speed steel roll is produced by use of a building up welding method or a continuous casting building up method (a high production cost being needed in each such method), an outer layer of the resulting roll can be rapidly solidified, without centrifugal force involved, with eventual protection of the roll against segregation of carbides but to an extent to invite a steep increase in production cost. In order to obviate the foregoing problems, the present inventors have previously made extensive researches on those high-speed steel rolls accruing from production by centrifugal casting (for example, Japanese Unexamined Patent Publication No. 5-1350, No. 8-73977, No. 9-41072 and the like). Experience gained by these inventors teaches that carbides would segregate particularly in a high composition range of Cr in which abrasion resistance could be conspicuously improved. In view of this problem, conventional practice has made it difficult to produce a high-speed steel roll at a low production cost and with a further enhancement in abrasion resistance.
One principal object of the present invention lies in the provision of a high-quality high-speed steel roll which is markedly excellent in abrasion resistance and rather free of carbide segregation even in the case of production by a centrifugal casting method of economical benefit.